Sounds like a fantastic way for law enforcement to get into your phone with probably cause. Random message you a benign picture from some rando account with a matching hash. Immediate capture for CP, data mine the phone, insert rootkit, 'so sorry about the time and money you lost - toodles'.
Warrants do have to name why, and where. However, anything they find along the way is fair game. If they open your trunk to find drugs and see a dead body, then the dead body is still admissible. (Assuming that the opening the trunk for drugs is okay.)
